Exported Value Field for Day Data Entry has 0 and 0+ As Defaults.Why?

Just noticed that the EXPOTED field value defaults have both 0 and 0± to choose from. Why? At first I thought I had mistakenly typed that and my browser was saving it for future use but upon deleting all cookies and data for the web site those 2 values remain. What is the point of the newly noticed 0± value in particular?